Reference signal sending method and communications device

ABSTRACT

A reference signal sending method and a communications device are provided. The reference signal sending method includes: generating, by a first device, a tracking reference signal, where the tracking reference signal corresponds to a DMRS port that is used by the first device when the first device sends data to a second device; mapping, by the first device, the tracking reference signal to a time-frequency resource that is used by the first device when the first device sends the data to the second device through the DMRS port, where the tracking reference signal is mapped to at least two modulation symbols on a same frequency resource in one transmission slot; and sending, by the first device, the tracking reference signal mapped to the time-frequency resource to the second device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/503,225, filed on Jul. 3, 2019, which is a continuation ofInternational Patent Application No. PCT/CN2018/071280, filed on Jan. 4,2018, which claims priority to Chinese Patent Application No.201710008210.9, filed on Jan. 5, 2017. All of the afore-mentioned patentapplications are hereby incorporated by reference in their entireties.

TECHNICAL FIELD

The present invention relates to the communications field, and morespecifically, to a reference signal sending method and a communicationsdevice.

BACKGROUND

In existing wireless communications networks (such as a 2G network, a 3Gnetwork, and a 4G network), all operating frequency bands ofcommunications systems fall within a frequency range below 6 GHz, andfewer operating frequency bands are available within this frequencyrange. Consequently, an ever-increasing communication requirement cannotbe met. On the contrary, a large quantity of frequency bands are notfully used within a frequency range above 6 GHz. Therefore, the industryis studying and developing a next-generation (for example, 5G) wirelesscommunications network whose operating frequency band is above 6 GHz, toprovide an ultrafast data communications service. Within the frequencyrange above 6 GHz, frequency bands that can be used in thenext-generation wireless communications network include frequency bandslocated at 28 GHz, 39 GHz, 60 GHz, 73 GHz, and the like. Because theoperating frequency band of the next-generation wireless communicationsnetwork is above 6 GHz, the next-generation wireless communicationsnetwork has notable features of a high-frequency communications system,such as high bandwidth and a highly-integrated antenna array, andtherefore easily implements a relatively high throughput. However,compared with the existing wireless communications networks, thenext-generation wireless communications network that operates within therange above 6 GHz is to suffer from severer intermediate radio frequencydistortion, especially impact of phase noise. In addition, impact of aDoppler effect and a central frequency offset (central frequency offset,CFO) on performance of the high-frequency communications system is alsoaggravated as a frequency band locates at a higher location. A commonfeature of the phase noise, the Doppler effect, and the CFO is that aphase error is introduced to data reception of the high-frequencycommunications system, and consequently the performance of thehigh-frequency communications system degrades and even thehigh-frequency communications system cannot operate.

SUMMARY

In view of this, this application provides a reference signal sendingmethod and a communications device, so that a receiving device thatreceives a reference signal can estimate a phase error of the signal,and further can compensate the received signal based on the phase error,thereby improving receiving performance of the receiving device.

According to an aspect of an embodiment of the present invention, areference signal sending method is provided. The method includes:

generating, by a first device, a tracking reference signal, where thetracking reference signal corresponds to a DMRS port that is used by thefirst device when the first device sends data to a second device, andthe tracking reference signal is used to track a phase changeexperienced by a tracking reference signal when the tracking referencesignal is transmitted on a channel corresponding to the DMRS port;

mapping, by the first device, the tracking reference signal to atime-frequency resource that is used by the first device when the firstdevice sends the data to the second device through the DMRS port, wherethe tracking reference signal is mapped to at least two modulationsymbols on a same frequency resource in one transmission slot; and

sending, by the first device, the tracking reference signal mapped tothe time-frequency resource to the second device.

According to another aspect of an embodiment of the present invention, acommunications device is provided. The communications device includes:

a processor, configured to generate a tracking reference signal, wherethe tracking reference signal corresponds to a DMRS port that is used bythe communications device when the communications device sends data, andthe tracking reference signal is used to track a phase changeexperienced by a tacking reference signal when the tracking referencesignal is transmitted on a channel corresponding to the DMRS port; andfurther configured to map the tracking reference signal to atime-frequency resource that is used by the communications device whenthe communications device sends the data through the DMRS port, wherethe tracking reference signal is mapped to at least two modulationsymbols on a same frequency resource in one transmission slot; and

a transceiver, configured to send the tracking reference signal mappedto the time-frequency resource.

In the technical solutions provided in the embodiments of the presentinvention, the tracking reference signal corresponding to the DMRS portthat is used when the data is sent is generated, and the trackingreference signal is mapped to the time-frequency resource that is usedwhen the data is sent through the DMRS port. Therefore, the trackingreference signal and other data transmitted through the DMRS port aretransmitted to a peer receiving device through a same channel, so thatthe peer receiving device can estimate the phase change of the trackingreference signal based on the received tracking reference signal, andfurther, can consider the estimated phase change as a phase change ofthe other data transmitted through the DMRS port, and compensate theother data by using the estimated phase change, to eliminate impact ofthe phase change on receiving performance of the receiving device,thereby improving the receiving performance of the receiving device.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an example schematic diagram of a communications systemaccording to an embodiment of the present invention;

FIG. 2 is an example flowchart of a reference signal sending methodaccording to an embodiment of the present invention;

FIG. 3A is an example schematic diagram of a structure of a resourceblock according to an embodiment of the present invention;

FIG. 3B is a schematic diagram of a location to which a trackingreference signal is mapped in a time-frequency resource according to anembodiment of the present invention;

FIG. 3C is a schematic diagram of another location to which a trackingreference signal is mapped in a time-frequency resource according to anembodiment of the present invention;

FIG. 4 is a schematic diagram of a reference signal sending methodaccording to an embodiment of the present invention;

FIG. 5 is another schematic diagram of a reference signal sending methodaccording to an embodiment of the present invention; and

FIG. 6 is an example schematic diagram of a hardware structure of acommunications device according to an embodiment of the presentinvention.

DESCRIPTION OF EMBODIMENTS

The following describes the technical solutions in the embodiments ofthe present invention with reference to the accompanying drawings in theembodiments of the present invention.

The following described technical solutions in the embodiments of thepresent invention are applied to a communications system. Thecommunications system may include one or more access control devices,and one or more user equipments (User Equipment, UE) that communicatewith each access control device. FIG. 1 shows an example of thecommunications system. The communications system shown in FIG. 1includes one access control device and a plurality of UEs thatcommunicate with the access control device.

The access control device may be any device that can directlycommunicate with the UE and that is configured to control the UE toaccess a communications network, such as a base station, a relaystation, or an access point. The base station may be a BTS (BaseTransceiver Station, base transceiver station) in a GSM (Global Systemfor Mobile communications, Global System for Mobile Communications)network or a CDMA (Code Division Multiple Access, Code Division MultipleAccess) network, an NB (NodeB) in a WCDMA (Wideband Code DivisionMultiple Access, Wideband Code Division Multiple Access) network, an eNBor an eNodeB (evolved NodeB) in LTE (Long Term Evolution, Long TermEvolution), a base station device in a next-generation (for example, 5G)wireless communications network, or the like.

The UE may be an access terminal, a subscriber unit, a subscriberstation, a mobile station, a remote station, a remote terminal, a mobiledevice, a user terminal, a terminal, a wireless communications device, auser agent, a user apparatus, or the like. The access terminal may be acellular phone, a cordless phone, a SIP (Session Initiation Protocol,Session Initiation Protocol) phone, a WLL (Wireless Local Loop, wirelesslocal loop) station, a PDA (Personal Digital Assistant, personal digitalassistant), a notebook computer, a tablet computer, a handheld devicehaving a wireless communication function, a computing device, anin-vehicle terminal, a wearable device, a terminal device in anext-generation (for example, 5G) wireless communications network, orthe like.

Communication between the access control device and the UE includesuplink signal transmission and downlink signal transmission. A frequencyband used for uplink signal transmission may be the same as or differentfrom a frequency band used for downlink signal transmission. Asdescribed in the background, when the frequency band used for uplinksignal transmission and the frequency band used for downlink signaltransmission are high frequency bands (in this application, allfrequency bands above 6 GHz are considered as high frequency bands) oruplink signal transmission and downlink signal transmission areperformed in another scenario in which severe phase distortion exists(for example, a high-speed railway), a severe phase error is introducedto signal reception due to, for example, phase noise, a Doppler effect,or a CFO, and consequently performance of the communications systemdegrades. In this case, the technical solutions provided in theembodiments of the present invention may be used to estimate the phaseerror, so that when a signal is received, the received signal iscompensated by using the estimated phase error.

An embodiment of the present invention provides a reference signalsending method. As shown in FIG. 2, the method includes the followingsteps.

S100. A first device generates a tracking reference signal, where thetracking reference signal corresponds to a DMRS (Demodulation ReferenceSignal, demodulation reference signal) port that is used by the firstdevice when the first device sends data to a second device. The trackingreference signal may be used to track a phase change experienced by atracking reference signal when the tracking reference signal istransmitted on a channel corresponding to the DMRS port. In thisembodiment of the present invention, the DMRS port is an antenna portassociated with a DMRS that has a specific pattern and/or sequence. TheDMRS may also be referred to as a UE specific RS (user specificreference signal), and the DMRS is used to demodulate user data. Forexample, for convenience, antenna ports 5, 7, 8, 9, 10, 11, 12, 13, 14,and the like in LTE are all referred to as DMRS ports in this embodimentof the present invention. In this embodiment of the present invention,the antenna port is a logical port rather than a physical port of aphysical antenna. For a definition of the antenna port, refer to arelated definition of “Antenna Port” in an existing LTE standard. Onetracking reference signal or at least two tracking reference signals maybe generated in this step, and one DMRS port or at least two DMRS portsmay be used by the first device when the first device sends the data tothe second device. A specific quantity of tracking reference signals anda specific quantity of DMRS ports may be determined based on aconfiguration of the first device. In this embodiment of the presentinvention, generating the tracking reference signal corresponding to theDMRS port actually represents configuring a corresponding trackingreference signal port for the DMRS port. A definition of the trackingreference signal port is similar to the definition of the DMRS port. Tobe specific, the tracking reference signal port is an antenna portassociated with a tracking reference signal that has a specific patternand/or sequence.

When only one DMRS port is configured when the first device sends thedata to the second device, the first device generates a trackingreference signal, namely, one tracking reference signal, correspondingto the DMRS port for the DMRS port, in other words, configures onecorresponding tracking reference signal port for the DMRS port.

When two or more DMRS ports used to send the data to the second deviceare configured for the first device, step S100 is generating acorresponding tracking reference signal for each of the DMRS ports. TheDMRS ports may correspond to a same tracking reference signal or maycorrespond to different tracking reference signals, in other words, theDMRS ports may correspond to a same tracking reference signal port ormay correspond to different tracking reference signal ports.

When there are two or more DMRS ports corresponding to a same trackingreference signal, step S100 may be generating a tracking referencesignal for only one of the ports, and considering the generated trackingreference signal as a tracking reference signal(s) corresponding to theother DMRS port(s). When a plurality of DMRS ports correspond to a sametracking reference signal, few overheads are occupied, thereby improvingcommunication efficiency. In an embodiment, if there arequasi-co-located DMRS ports, these quasi-co-located DMRS ports maycorrespond to a same tracking reference signal. To be specific, thefirst device needs to generate a tracking reference signal for only oneof the DMRS ports, and then consider the tracking reference signal as atracking reference signal(s) corresponding to the other DMRS port(s). Inthis embodiment of the present invention, if there are quasi-co-locatedDMRS ports, it indicates that data transmitted through these DMRS portsexperiences a same phase change. In an embodiment of the presentinvention, an antenna port (namely, the tracking reference signal port)associated with the tracking reference signal in step S100 and the DMRSport are also quasi-co-located. In this embodiment of the presentinvention, the tracking reference signal is a type of reference signal,and is a predefined signal known to both communications parties (namely,the first device and the second device).

S102. The first device maps the tracking reference signal to atime-frequency resource that is used by the first device when the firstdevice sends the data to the second device through the DMRS port, wherethe tracking reference signal is mapped to at least two modulationsymbols on a same frequency resource in one transmission slot.

In this embodiment of the present invention, the time-frequency resourceis similar to a time-frequency resource in existing LTE, and is a radioresource that includes time and frequency and that is used to transmit asignal. The time-frequency resource that is used by the first devicewhen the first device sends the data to the second device through theDMRS port may include one or more resource blocks (RB, Resource Block).The RB includes a fixed quantity of subcarriers in frequency domain andoccupies one transmission slot in time domain. Bandwidth represented bythe fixed quantity of subcarriers is referred to as transmissionbandwidth of the RB. The resource block includes a fixed quantity ofresource elements (RE, Resource Element). Each resource element occupiesone subcarrier in frequency domain and occupies duration of onemodulation symbol in time domain. FIG. 3A shows an example of the RB,where a vertical axis represents subcarrier frequency and a horizontalaxis represents time. The RB includes 12×14 small grids, each small gridrepresents one RE, and the RB occupies duration of 14 modulation symbolson 12 subcarriers. In this embodiment of the present invention, themodulation symbol may be an OFDM (Orthogonal Frequency DivisionMultiplexing, orthogonal frequency division multiplexing) symbol, or maybe a symbol generated in another modulation scheme.

In this embodiment of the present invention, mapping the trackingreference signal to the time-frequency resource means determining, inthe time-frequency resource, a location at which an RE is used totransmit the tracking reference signal, and modulating, within durationcorresponding to the RE, the tracking reference signal to a subcarriercorresponding to the RE, to form a modulation symbol.

The same frequency resource may be one subcarrier or may be a pluralityof subcarriers. If the same frequency resource is a plurality ofsubcarriers, the at least two modulation symbols on the same frequencyresource mean that there are at least two modulation symbols on eachsubcarrier.

If at least two tracking reference signals are generated in step S100,in step S102, each tracking reference signal needs to be mapped to atleast two modulation symbols on a same frequency resource in onetransmission slot. However, the plurality of tracking reference signalsmay be mapped to a same frequency resource or may be mapped to differentfrequency resources. If different tracking reference signals are mappedto a same frequency resource, the different tracking reference signalsmay be mapped to different modulation symbols or may be mapped to a samemodulation symbol. When different tracking reference signals are mappedto a same modulation symbol on a same frequency resource, specifically,precoding is first separately performed on these different trackingreference signals, then precoded tracking reference signals aresuperposed, and finally, a result obtained after the superposing ismapped to the time-frequency resource.

In an embodiment, when at least two DMRS ports used by the first deviceto send the data to the second device are allocated, in step S102,tracking reference signals corresponding to at least two of the at leasttwo DMRS ports may be mapped to a same frequency resource, or trackingreference signals corresponding to different DMRS ports may be mapped todifferent frequency resources. In a specific example, as shown in FIG.3B, four DMRS ports are used by the first device to send the data to thesecond device, and numbers of the four DMRS ports are i, i+1, i+2, andi+3, respectively. All tracking reference signals generated for all theDMRS ports are mapped to a same frequency resource, for example, REsidentified by a number j that are shown in FIG. 3B. In another specificexample, as shown in FIG. 3C, a tracking reference signal generated fora DMRS port numbered i and a tracking reference signal generated for aDMRS port numbered i+1 are mapped to a same frequency resource, forexample, REs identified by a number j+1 in FIG. 3C, and a trackingreference signal generated for a DMRS port numbered i+2 and a trackingreference signal generated for a DMRS port numbered i+3 are mapped toanother frequency resource, for example, REs identified by a number j inFIG. 3C. It can be learned from FIG. 3B and FIG. 3C that differenttracking reference signal ports may share a same time-frequencyresource, or may occupy different time-frequency resources.

In a specific example, one DMRS port is used by the first device whenthe first device sends the data to the second device, the time-frequencyresource allocated to the first device for sending the data to thesecond device through the DMRS port is one RB, and one trackingreference signal is generated for the DMRS port. As shown in FIG. 3A,REs identified by oblique stripes in the RB each are a time-frequencyresource allocated to the DMRS port for transmitting a DMRS, REsidentified by meshes each are a time-frequency resource used to send thegenerated tracking reference signal, in other words, each are atime-frequency resource location to which the tracking reference signalis mapped, and the other REs may be used to transmit other data. In FIG.3A, the tracking reference signal is mapped to consecutive modulationsymbols on one subcarrier. It may be understood that the trackingreference signal may be mapped to inconsecutive modulation symbols onone subcarrier.

Step S104: The first device sends the tracking reference signal mappedto the time-frequency resource to the second device.

In this embodiment, the tracking reference signal corresponding to theDMRS port that is used by the first device when the first device sendsthe data to the second device is generated, and the tracking referencesignal is mapped to the time-frequency resource that is used by thefirst device when the first device sends the data to the second devicethrough the DMRS port. Therefore, the tracking reference signal andother data transmitted through the DMRS port are transmitted to thesecond device through a same channel, so that the second device canestimate the phase change of the tracking reference signal based on thereceived tracking reference signal, and further, can consider theestimated phase change as a phase change of the other data transmittedthrough the DMRS port, and compensate the other data by using theestimated phase change, to eliminate impact of the phase change onreceiving performance of the second device, thereby improving thereceiving performance of the second device.

In a specific embodiment, estimating the phase change of the trackingreference signal is specifically estimating a measurement of signaldistortion caused by the phase change, for example, a CPE (Common PhaseError, common phase error) or ICI (Inter-Carrier Interference,inter-carrier interference). In an actual communications system, impactof the ICI on performance of the communications system is less thanimpact of the CPE on the performance of the communications system.Therefore, generally, only the CPE is considered for compensation.

An example in which OFDM modulation is used when the first device sendsthe data to the second device is used below to briefly describe aprinciple depending on which the second device estimates the CPE basedon the received tracking reference signal.

The second device receives an OFDM symbol, and obtains a signal y_(j)(n)after performing processing such as CP removal and FFT processing on theOFDM symbol. y_(j)(n) may be described by using the followingmathematical model:

$\begin{matrix}{{y_{j}(n)} = {{{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{j}(n)}{V_{i}(n)}{s_{i}(n)}}} + {Z_{j}(n)}} = {{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{i,j}^{eff}(n)}{s_{i}(n)}}} + {Z_{f}(n)}}}} & (1)\end{matrix}$

y_(j)(n) represents a signal received on an n^(th) subcarrier on aj^(th) receive antenna of the second device, i represents a number of adata stream, and M represents a quantity of data streams. H_(j)(n)represents a channel coefficient vector of the j^(th) receive antenna ofthe second device on the n^(th) subcarrier, a dimension of H_(j)(n) is1*N_(TX), and N_(TX) represents a quantity of transmit antennas of thefirst device. V_(i)(n) is a precoding vector of an i^(th) data stream onthe n^(th) subcarrier, and V_(i)(n) is an N_(TX)*1 vector. s_(i)(n)represents a transmit symbol of the i^(th) data stream on the n^(th)subcarrier. Z_(j)(n) represent interference and noise on the n^(th)subcarrier on the j^(th) receive antenna. α_(i,j) indicates a CPE causedby a phase change on the i^(th) data stream on the j^(th) receiveantenna, and α_(i,j) is a complex scalar. H_(i,j) ^(eff)(n) is anequivalent channel coefficient, and specifically H_(i,j)^(eff)(n)=H_(j)(n)V_(i)(n). H_(i,j) ^(eff)(n) represents a product ofthe channel coefficient vector and the precoding vector, and may beestimated by using a DMRS. It should be noted that there is a one-to-onecorrespondence between a data stream and a DMRS port.

When the model is used to represent a received OFDM symbol that isgenerated based on data, the transmit symbol s_(i)(n) of the firstdevice has different values on different data streams, and the valuesare unknown to the second device. When the model is used to represent areceived OFDM symbol that is generated based on a tracking referencesignal, because the tracking reference signal is agreed on by both thefirst device and the second device in advance and is known to bothparties, s_(i)(n) is known on a side of the second device. Therefore,H_(i,j) ^(eff)(n) and s_(i)(n) in formula (1) are known.

When the first device sends only one data stream to the second device(in other words, M=1), α_(i,j) may be estimated by using formula (1).

When the first device sends a plurality of data streams to the seconddevice (in other words, M>1), there are a plurality of values ofα_(i,j), and the first device can generate a plurality of trackingreference signals. After receiving the plurality of tracking referencesignals, the second device may combine the plurality of trackingreference signals to estimate all the values of α_(i,j), to be specific:

$\begin{matrix}\left\{ \begin{matrix}{{y_{j}\left( n_{1} \right)} = {{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{j}\left( n_{1} \right)}{V_{i}(n)}{s_{i}\left( n_{1} \right)}}} + {Z_{j}\left( n_{1} \right)}}} \\{{y_{j}\left( n_{2} \right)} = {{\sum\limits_{i = 1}^{M}{\alpha_{i,j}H_{j}{j\left( n_{2} \right)}{V_{i}\left( n_{2} \right)}{s_{i}\left( n_{1} \right)}}} + {Z_{j}\left( n_{2} \right)}}} \\\vdots \\{{y_{j}\left( n_{T} \right)} = {{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{j}\left( n_{T} \right)}{V_{i}\left( n_{2} \right)}{s_{i}\left( n_{T} \right)}}} + {Z_{j}\left( n_{T} \right)}}}\end{matrix} \right. & (2)\end{matrix}$

T is a quantity of symbols that are generated based on trackingreference signals in one OFDM symbol, n_(k) represents a number of asubcarrier on which a k^(th) tracking reference signal is located, andk=1, 2, . . . , T.

To simplify processing of the foregoing system of equations, the firstdevice may set tracking reference signals in all data streams on a samesubcarrier to a same one. To be specific, in formula (1), s_(i)(n)=p(n),1≤i≤M, and p(n) represents an RS symbol. In this case, formula (1) maybe expressed as:

$\begin{matrix}{{y_{j}(n)} = {{{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{j}(n)}{V_{i}(n)}{p(n)}}} + {Z_{j}(n)}} = {{{p(n)}{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{j}(n)}{V_{i}(n)}}}} + {Z_{j}(n)}}}} & (3)\end{matrix}$

Because p(n) is known on the side of the second device,

$\begin{matrix}{{{\hat{y}}_{j}(n)} = {\frac{y_{j}(n)}{p(n)} = {{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{j}(n)}{V_{i}(n)}}} + {\frac{Z_{j}(n)}{p(n)}.}}}} & (4)\end{matrix}$

Correspondingly, the system (2) of equations may be processed into thefollowing system of equations:

$\begin{matrix}{\left\{ {{\begin{matrix}{{{\overset{\hat{}}{y}}_{j}\left( n_{1} \right)} = {{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{j}\left( n_{1} \right)}{V_{i}\ \left( n_{1} \right)}}} + \frac{Z_{j}\left( n_{1} \right)}{p\left( n_{1} \right)}}} \\{{{\overset{\hat{}}{y}}_{j}\left( n_{2} \right)} = {{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{j}\left( n_{2} \right)}{V_{i}\ \left( n_{2} \right)}}} + \frac{Z_{j}\left( n_{2} \right)}{p\left( n_{2} \right)}}} \\{{{\overset{\hat{}}{y}}_{j}\left( n_{T} \right)} = {{\sum\limits_{i = 1}^{M}{\alpha_{i,j}{H_{j}\left( n_{T} \right)}{V_{i}\ \left( n_{T} \right)}}} + \frac{Z_{j}\left( n_{T} \right)}{p\left( n_{T} \right)}}}\end{matrix}T} \geq M} \right..} & (5)\end{matrix}$

In the foregoing system of equations, a value of α_(i,j) may beestimated by using an existing algorithm such as ZF (Zero Forcing, zeroforcing) or an MMSE (Minimum Mean Square Error, minimum mean squareerror).

The second device can compensate, based on the estimated CPE, for aphase error that is generated when the second device receives the data,thereby improving receiving performance of the second device.

The method described in the embodiment shown in FIG. 2 may be applied tothe communications system shown in FIG. 1. When the method is applied todownlink signal transmission between an access control device and UE,the first device is the access control device, and the second device isthe UE. When the method is applied to uplink signal transmission betweenthe access control device and the UE, the first device is the UE, andthe second device is the access control device.

An embodiment of the present invention further provides anotherreference signal sending method. As shown in FIG. 4, the method may beapplied to uplink signal transmission in the communications system shownin FIG. 1, and includes the following steps:

Step S106: UE receives first indication information sent by an accesscontrol device, where the first indication information is used toinstruct the UE to generate a tracking reference signal corresponding toa DMRS port that is used by the UE when the UE sends data to the accesscontrol device.

A lower-order modulation scheme (for example, a modulation scheme whosemodulation order is lower than or equal to 16) or a higher-ordermodulation scheme (for example, a modulation scheme whose modulationorder is higher than 16) may be used by the UE when the UE sends thedata to the access control device through the DMRS port. When the UEperforms uplink transmission in the lower-order modulation scheme, whenreceiving the data sent by the UE, the access control device isinsensitive to a phase error caused by phase noise. In this case, the UEmay not need to send the tracking reference signal, and the accesscontrol device may still correctly receive the data sent by the UE. Whenthe UE performs uplink transmission in the higher-order modulationscheme, when receiving the data sent by the UE, the access controldevice is very sensitive to a phase error caused by phase noise. In thiscase, the UE needs to send the tracking reference signal, so that theaccess control device estimates the phase error on the data based on thetracking reference signal, and compensates the received data based onthe phase error, thereby improving receiving performance of the accesscontrol device. In view of this, the access control device maydetermine, based on an actual requirement, whether the access controldevice needs to send the first indication information to the UE. When amodulation scheme that is used by the UE to send the data to the accesscontrol device through the DMRS port is specified by the access controldevice, the access control device needs to send the first indicationinformation to the UE. It may be understood that, in some embodiments,the first indication information may not be sent, for example, when theUE can self-determine a modulation scheme that is used by the UE duringuplink signal transmission, when the UE and the access control devicejointly comply with a specific protocol and the protocol specifies thatthe first indication information does not need to be sent, or when onlythe higher-order modulation scheme is used by the first device when thefirst device sends the data to the second device.

The first indication information may be implemented in a plurality ofmanners, and the plurality of manners may be classified into two types:an explicit indication manner and an implicit indication manner.

In the explicit indication manner, a dedicated message that is used bythe access control device to instruct the UE to generate the trackingreference signal corresponding to the DMRS port may be set; or a flagbit may be set in an idle field in a control message sent by the accesscontrol device to the UE, to notify, by using the flag bit, the UEwhether the UE needs to generate the tracking reference signal. Thecontrol message may be an existing physical layer control message suchas DCI (Downlink Control Information, downlink control information), ormay be an existing non-physical layer control message such as MAC CE(Media Access Control CE, MAC control element) signaling or RRC (RadioResource Control, Radio Resource Control) signaling.

In the implicit indication manner, an indication function of the firstindication information may be implemented by using MCS (Modulation andCoding Scheme, modulation and coding scheme) information that is sent bythe access control device to the UE and that is used to notify the UE ofa modulation scheme that should be used by the UE when the UE sendsdata. For example, when an order of the modulation scheme indicated bythe MCS information is higher than 2 (for example, a modulation schemecorresponding to a modulation order 2 is QPSK modulation) or is higherthan 4 (for example, a modulation scheme corresponding to a modulationorder 4 is 16QAM), it is considered that the UE needs to send thetracking reference signal; or when an order of the modulation schemeindicated by the MCS information is lower than or equal to 2 or is lowerthan or equal to 4, the UE does not need to send the tracking referencesignal. The manner in which the MCS information is used to indicatewhether the tracking reference signal needs to be sent achieves reuse ofthe MCS information, so that overheads can be reduced, thereby improvingcommunication or when an order of the modulation scheme indicated by theMCS information is lower than or equal to 2 or is lower than or equal to4 efficiency. It may be understood that the implicit indication manneris not limited to the listed one, and there may be other manners. Theother manners are not enumerated herein.

When receiving the first indication information for instructing the UEto send the tracking reference signal, the UE performs the methodprovided in the embodiment shown in FIG. 2. Details are not describedherein again.

In an embodiment, as shown in FIG. 4, the method may further include:

Step S108: Before step S100, the UE receives second indicationinformation sent by the access control device, where the secondindication information is used to indicate a quantity of trackingreference signals that need to be generated by the UE for the DMRS port.Correspondingly, after receiving the second indication information, instep S100, the UE generates tracking reference signals of the quantityindicated by the second indication information.

In a specific implementation, the second indication information may beimplemented in an explicit indication manner, or the second indicationinformation may be implemented in an implicit indication manner. In animplementation of the explicit indication manner, the second indicationinformation clearly indicates the quantity of tracking reference signalsthat need to be generated by the UE. In an implementation of theimplicit indication manner, the second indication information does notclearly indicate the quantity of tracking reference signals that need tobe generated by the UE, and the UE can know the quantity of trackingreference signals that need to be generated, only by processing thesecond indication information after receiving the second indicationinformation.

In an implementation of the implicit indication manner, the secondindication information specifically includes resource schedulinginformation that is used to indicate a quantity of time-frequencyresources that are used by the UE when the UE sends the data to theaccess control device through the DMRS port, and the quantity oftracking reference signals that need to be generated by the UE isdetermined based on the quantity of time-frequency resources that isindicated by the resource scheduling information. In this embodiment ofthe present invention, the quantity of time-frequency resources may berepresented by a quantity of resource blocks. For example, differentranges of a quantity of time-frequency resources that are used whenuplink signal transmission is performed through a DMRS port respectivelycorrespond to different quantities of tracking reference signals, andthe UE may prestore the correspondence, or the UE obtains thecorrespondence from the access control device in advance.

In an embodiment, when the time-frequency resource indicated by theresource scheduling information is n resource blocks, and N₁≤n≤N₂, theUE needs to generate M tracking reference signals. N₁ and N₂ havedifferent values, and correspondingly, M also has different values.Table 1 shows an example of the correspondence. It may be understoodthat, in another embodiment, N₁, N₂, and M may alternatively have othervalues. This is not limited in the present invention. In this embodimentof the present invention, the following table shows an example of acorrespondence between a quantity of time-frequency resources that areused when uplink signal transmission is performed by using a DMRS portand a quantity of tracking reference signals corresponding to the DMRSport.

TABLE 1 Quantity n of Quantity M of resource blocks tracking referencesignals 1 ≤ n ≤ 4 1 5 ≤ n ≤ 8 2  9 ≤ n ≤ 12 3  13 ≤ n ≤ 100 4

The UE may prestore or obtain, in advance, the correspondence in Table 1or a correspondence similar to the correspondence in Table 1 from theaccess control device.

After receiving the resource scheduling information, the UE maycompare/query Table 1 with/based on a value of the quantity n ofresource blocks in the resource scheduling information, to obtain thequantity of tracking reference signals that need to be generated.

In another embodiment, the following manner may alternatively be used bythe UE when the UE determines the quantity of tracking reference signalsbased on the quantity of time-frequency resources that are indicated bythe resource scheduling information:

M=└n·α┘ or ┌n·α┐  (7)

└ ┘ represents rounding down, ┌ ┐ represents rounding up, and α is avalue from 0 to 1 (including 0 and 1). A value of α may be prestored inthe UE, or may be sent by the access control device to the UE inadvance. In a specific example, the value of α may be set to ¼.

It may be understood that, in an implementation of the explicitindication manner of the second indication information, the accesscontrol device may also calculate the quantity of tracking referencesignals that need to be generated based on Table 1 or formula (7), andthen notify the UE of the calculated result by using the secondindication information.

In most cases, all time-frequency resources used by the UE during uplinksignal transmission need to be allocated by the access control device.Therefore, in these cases, the access control device inevitably needs tonotify the UE of an allocated result by using the resource schedulinginformation. In this embodiment, the quantity of tracking referencesignals that need to be generated by the UE is indicated by reusing theresource scheduling information, so that overheads are reduced, therebyimproving communication efficiency. In addition, the quantity oftracking reference signals is related to the quantity of time-frequencyresources. The solution provided in this embodiment can ensure that theaccess control device accurately estimates the phase error, withoutoccupying excessive overheads.

As shown in FIG. 4, the method may further include: Step S110: The UEreceives third indication information sent by the access control device,where the third indication information is used to indicate a location towhich the tracking reference signal corresponding to the DMRS portshould be mapped in a time-frequency resource. Correspondingly, afterreceiving the third indication information, in step S102, the UE mapsthe tracking reference signal to the location that is in thetime-frequency resource and that is indicated by the third indicationinformation. It should be understood that, if there are a plurality oftracking reference signals, locations that are in the time-frequencyresource and to which all the tracking reference signals should bemapped may be indicated by using one piece of third indicationinformation, or one piece of third indication information may be sentfor each tracking reference signal.

The access control device determines, based on the quantity oftime-frequency resources (the quantity n of resource blocks) allocatedto the UE for uplink signal transmission and the quantity M of trackingreference signals that need to be generated, a location to which eachtracking reference signal should be mapped in the time-frequencyresource. The access control device consecutively numbers the n resourceblocks 0, 1, 2, . . . , and N in ascending order of subcarrierfrequency, where N=n−1. The access control device may determine, basedon formula (8), a number of a resource block to which each trackingreference signal should be mapped:

$\begin{matrix}{{N_{k} = {{{\left\lfloor \frac{N + 1}{M} \right\rfloor \cdot k} + {\Delta\mspace{14mu}{or}\mspace{20mu} N_{k}}} = {{\left\lceil \frac{N + 1}{M} \right\rceil \cdot k} + \Delta}}},{{{where}\mspace{14mu} 0} \leq k \leq {M - 1}}} & (8)\end{matrix}$

k is a number of a tracking reference signal, and N_(k) is a number of aresource block to which the tracking reference signal numbered k shouldbe mapped. Δ represents an offset. Δ may be 0, may be another presetvalue, or may be a specific value related to the UE (for example, avalue calculated by using a UE-ID, or a value notified by the accesscontrol device to the UE).

When a value of Δ makes a value of N_(k) calculated by using formula (8)exceed the maximum resource block number N, the number of the resourceblock to which each tracking reference signal should be mapped may bedetermined based on formula (9):

$\begin{matrix}{{N_{k} = {{{mod}\ \left( {{{\left\lceil \frac{N + 1}{M} \right\rceil \cdot k} + \Delta},\ N} \right)}\mspace{14mu}{or}}}{N_{k} = {{mod}\ \left( {{{\left\lfloor \frac{N + 1}{M} \right\rfloor \cdot k} + \Delta},\ N} \right)}}} & (9)\end{matrix}$

mod(x, y) represents a modulo operation, and mod(x, y) returns aremainder obtained after x is divided by y. It should be noted thatformula (9) is applicable to the present invention regardless of a valueof Δ.

When the resource block to which each tracking reference signal ismapped is determined, the determining manner shown in formula (8) or (9)can implement pseudo-randomization of the location to which the trackingreference signal is mapped, thereby reducing interference between users.

The access control device may notify the UE of the calculated result byusing the third indication information, and in step S102, the UE mapsthe tracking reference signal to the time-frequency resource based onthe calculated result. Further, a specific subcarrier to which eachtracking reference signal is mapped in the resource block correspondingto each tracking reference signal may be specified by the access controldevice, or may be specified in a protocol with which the access controldevice and the UE jointly comply. In another embodiment, the accesscontrol device may notify the UE of the result calculated by usingformula (8) or (9). Provided that the UE obtains parameters such as Nand M that are needed when the mapping location is calculated by usingformula (8) or (9), the UE can calculate the resource block to whicheach tracking reference signal is mapped. In this case, the thirdindication information needs to carry only the parameters N and M, andeven the second indication information that includes the resourcescheduling information is directly used as the third indicationinformation.

As shown in FIG. 4, the method may further include: Step S112: The UEreceives fourth indication information sent by the access controldevice, where the fourth indication information is used to indicate thetracking reference signal corresponding to the DMRS port.Correspondingly, in step S100, the UE generates the tracking referencesignal indicated by the fourth indication information.

It may be understood that there is no sequence among steps S106, S108,S110, and S112. In another embodiment, the four steps are not allneeded. For example, when the access control device sends any one pieceof the second indication information, the third indication information,and the fourth indication information, it is considered by default thatthe UE needs to generate the tracking reference signal and send thetracking reference signal to the access control device. In this case,the access control device does not need to send the first indicationinformation.

In another embodiment, for a specific DMRS port, the UE can entirelyindependently determine whether a tracking reference signal needs to begenerated, a quantity of tracking reference signals that need to begenerated, a type of tracking reference signal that needs to begenerated, and a specific location to which each tracking referencesignal should be mapped in a time-frequency resource. In thisembodiment, none of steps S106, S108, S110, and S110 may be needed. Inthis embodiment, for a process in which the UE independently determinesthe foregoing four pieces of information, refer to the foregoingdescribed process in which the access control device determines theforegoing pieces of information. Details are not described herein again.The UE may send the four pieces of information independently determinedby the UE to the access control device.

It should be noted that the first indication information, the secondindication information, the third indication information, and the fourthindication information may be separately sent, or may be included in asame message.

An embodiment of the present invention further provides anotherreference signal sending method. The method may be applied to downlinksignal transmission in the communications system shown in FIG. 1. Asshown in FIG. 5, in addition to the steps in the embodiment shown inFIG. 2, the method may further include at least one of steps S114, S116,S118, S120, and S122.

Step S114: An access control device determines, based on atime-frequency resource that is used by the access control device whenthe access control device sends data to the UE through a DMRS port, aquantity of tracking reference signals corresponding to the DMRS portthat need to be generated.

When sending the data to the UE through the DMRS port, the accesscontrol device allocates the time-frequency resource to the DMRS port.In this step, the access control device may determine, based on thetime-frequency resource, the quantity of tracking reference signals thatneed to be generated for the DMRS port. For a specific process in whichthe access control device determines the quantity of tracking referencesignals based on the time-frequency resource, refer to the process ofdetermining the quantity of tracking reference signals in the embodimentshown in FIG. 4. Details are not described herein again. In thisembodiment, the quantity of tracking reference signals that need to begenerated is determined based on a quantity of time-frequency resources.In another embodiment, the quantity of tracking reference signals thatneed to be generated may alternatively be determined based on anothercommunication parameter, for example, a type of the UE, or an MCS thatis used by the access control device when the access control devicesends the data to the UE through the DMRS port.

Correspondingly, in step S100, the access control device generatestracking reference signals of the quantity determined in step S114.

When it is determined in step S114 that at least two tracking referencesignals need to be generated, step S102 may include:

Step S1021: The access control device determines a location to whicheach tracking reference signal is mapped in the time-frequency resource.

Step S1022: The access control device maps each tracking referencesignal to the time-frequency resource based on the determined location.

In the embodiment shown in FIG. 5, step S1021 is performed after stepS100. It may be understood that in another embodiment, step S1201 mayalternatively be performed before step S100.

Step S116: The access control device sends fifth indication informationto the UE, where the fifth indication information is used to indicatethat the tracking reference signal is sent on the time-frequencyresource that is used by the access control device when the accesscontrol device sends the data to the UE through the DMRS port.

As described in the embodiment shown in FIG. 4, the access controldevice does not need to send the tracking reference signal to the UE inall cases. Generally, the access control device needs to send thetracking reference signal to the UE only when the access control devicesends the data to the UE in a higher-order modulation scheme. Certainly,when the access control device sends the data to the UE in a lower-ordermodulation scheme, the access control device may also send the trackingreference signal to the UE. However, receiving performance of the UE isnot improved significantly, and relatively high overheads are occupied.This reduces communication efficiency.

When only the higher-order modulation scheme is used for downlink signaltransmission in the communications system shown in FIG. 1, it isconsidered by default that the UE knows that the access control devicecertainly sends the tracking reference signal. In this case, the accesscontrol device does not need to send the fifth indication information,in other words, does not need to perform step S116.

When the higher-order modulation scheme or the lower-order modulationscheme may be used for downlink signal transmission in thecommunications system shown in FIG. 1, the access control device needsto notify the UE whether the access control device sends the trackingreference signal to the UE, so that the UE determines whether the UEneeds to receive the tracking reference signal. In this case, when theaccess control device performs downlink signal transmission in thehigher-order modulation scheme, the access control device may send thefifth indication information to the UE. When the access control deviceperforms downlink signal transmission in the lower-order modulationscheme, the access control device may not send the fifth indicationinformation, or may send indication information that is used to indicatethat the tracking reference signal is not sent. If the UE receives nofifth indication information or receives the indication information thatis used to indicate that the tracking reference signal is not sent, theUE does not need to receive the tracking reference signal.

For a specific implementation of the fifth indication information, referto the implementation of the first indication information. Details arenot described herein again.

Step S118: The access control device sends sixth indication informationto the UE, where the sixth indication information is used to indicatethe quantity of tracking reference signals corresponding to the DMRSport. For a specific implementation of the sixth indication information,refer to the implementation of the second indication information in theembodiment shown in FIG. 4. Details are not described herein again.

Step S120: The access control device sends seventh indicationinformation to the UE, where the seventh indication information is usedto indicate a location to which the tracking reference signal is mappedin the time-frequency resource. For a specific implementation of theseventh indication information, refer to the implementation of the thirdindication information in the embodiment shown in FIG. 4. Details arenot described herein again.

Step S122: The access control device sends eighth indication informationto the UE, where the eighth indication information is used to indicatethe tracking reference signal corresponding to the DMRS port. Generally,a plurality of tracking reference signals can be used by the accesscontrol device and the UE. A tracking reference signal or trackingreference signals that is or are selected by the access control deviceis or are notified to the UE, so that the UE can directly receive thetracking reference signal based on the tracking reference signalindicated by the eighth indication information, to avoid blind detectionon the tracking reference signal, thereby improving processingefficiency of the UE during signal reception.

When the access control device sends any one piece of the sixthindication information, the seventh indication information, and theeighth indication information, the access control device mayalternatively not send the fifth indication information, because thesixth indication information, the seventh indication information, andthe eighth indication information all imply that the access controldevice sends the tracking reference signal.

In addition to the order shown in FIG. 5, step S118, step S120, and stepS122 may alternatively be performed in another different order, providedthat step S118, step S120, and step S122 are performed before step S104.

An embodiment of the present invention further provides a communicationsdevice. As shown in FIG. 6, the communications device includes aprocessor 10 and a transceiver 20.

The processor 10 is configured to generate a tracking reference signal,where the tracking reference signal corresponds to a DMRS port that isused by the communications device when the communications device sendsdata, and the tracking reference signal is used to track a phase changeexperienced by a tracking reference signal when the tracking referencesignal is transmitted on a channel corresponding to the DMRS port; andis further configured to map the tracking reference signal to atime-frequency resource that is used by the communications device whenthe communications device sends the data through the DMRS port, wherethe tracking reference signal is mapped to at least two modulationsymbols on a same frequency resource in one transmission slot.

The transceiver 20 is configured to send the tracking reference signalmapped to the time-frequency resource.

It may be learned from the foregoing embodiments that the communicationsdevice shown in FIG. 6 performs the method provided in the embodimentshown in FIG. 2. Specifically, the processor 10 performs step S100 andstep S102 in the embodiment shown in FIG. 2, and the transceiver 20performs step S104 in the embodiment shown in FIG. 2. Therefore, formore details about performing the foregoing steps by the processor 10and the transceiver 20, refer to the related descriptions in theembodiment shown in FIG. 2. Details are not described herein again.

The communications device generates the tracking reference signalcorresponding to the DMRS port that is used by the communications devicewhen the communications device sends the data, and maps the trackingreference signal to the time-frequency resource that is used when thedata is sent through the DMRS port, where the tracking reference signalis mapped to at least two modulation symbols on a same frequencyresource in one transmission slot. Therefore, the tracking referencesignal and other data transmitted through the DMRS port are transmittedto a peer device through a same channel, so that the peer device canestimate the phase change of the tracking reference signal based on thereceived tracking reference signal, and further, can consider theestimated phase change as a phase change of the other data transmittedthrough the DMRS port, and compensate the other data symbols by usingthe estimated phase change, to eliminate impact of the phase change onreceiving performance of the peer device, thereby improving thereceiving performance of the peer device.

The communications device shown in FIG. 6 may be further applied to thecommunications system shown in FIG. 1. When the communications device isapplied to downlink signal transmission between an access control deviceand UE, the communications device is the access control device, and thepeer device is the UE. When the communications device is applied touplink signal transmission between the access control device and the UE,the communications device is the UE, and the peer device is the accesscontrol device.

An embodiment of the present invention provides UE. The UE includes theprocessor 10 and the transceiver 20 that are shown in FIG. 6. Whenperforming uplink signal transmission with an access control device, theUE may generate a tracking reference signal and send the trackingreference signal to the access control device. Specifically, the UE maybe configured to perform the reference signal sending method provided inthe embodiment shown in FIG. 4.

During uplink signal transmission, in addition to step S104 in theembodiment shown in FIG. 2, the transceiver 20 of the UE may be furtherconfigured to perform step S106, step S108, step S110, and step S112 inthe embodiment shown in FIG. 4, in other words, configured to receivefirst indication information, second indication information, a thirdindication information, and a fourth indication formation. It should benoted that, in another embodiment, the transceiver 20 of the UE mayperform some of step S106, step S108, step S110, and step S112, and evenperform none of step S106, step S108, step S110, and step S112.

After receiving any one of the foregoing four pieces of indicationinformation, the transceiver 20 of the UE provides the indicationinformation to the processor 10, and the processor 10 performscorresponding processing based on the indication information. For theprocessing performed by the processor 10 of the UE based on the receivedindication information, refer to the related descriptions in theembodiment shown in FIG. 4. Details are not described herein again.

An embodiment of the present invention further provides an accesscontrol device. The access control device includes the processor 10 andthe transceiver 20 that are shown in FIG. 6. When performing downlinksignal transmission with UE, the access control device may generate atracking reference signal and send the tracking reference signal to theUE. Specifically, the access control device may be configured to performthe reference signal sending method provided in the embodiment shown inFIG. 5.

During downlink signal transmission, in addition to step S104 in theembodiment shown in FIG. 2, the transceiver 20 of the access controldevice may be further configured to perform step S116, step S118, stepS120, and step S122 in the embodiment shown in FIG. 5, in other words,configured to send fifth indication information, sixth indicationinformation, a seventh indication information, and an eighth indicationinformation. It should be noted that, in another embodiment, thetransceiver 20 of the access control device may perform only some ofstep S116, step S118, step S120, and step S122, and even perform none ofstep S116, step S118, step S120, and step S122. It may be understoodthat the foregoing four pieces of indication information are generatedby the processor 10 of the access control device, and then sent by thetransceiver of the access control device.

The processor 10 of the access control device may be further configuredto perform step S114 in the embodiment in FIG. 5, to be specific,determine, based on a time-frequency resource that is used by the accesscontrol device when the access control device sends data by using a DMRSport, a quantity of tracking reference signals corresponding to the DMRSport that need to be generated.

When the processor 10 of the access control device determines that atleast two tracking reference signals need to be generated, whenperforming step S102, the processor 10 of the access control devicefirst determines a location to which each tracking reference signal ismapped in the time-frequency resource, and then maps each trackingreference signal to the time-frequency resource based on the determinedlocation.

For a specific process in which the processor 10 and the transceiver 20of the access control device perform the foregoing steps, refer to therelated descriptions in the embodiments shown in FIG. 2 and FIG. 5.Details are not described herein again.

In the embodiments of the present invention, the processor 10 may be ageneral purpose processor, for example, but is not limited to, a centralprocessing unit (Central Processing Unit, CPU), or may be a dedicatedprocessor, for example, but is not limited to, a digital signalprocessor (Digital Signal Processor, DSP), an application-specificintegrated circuit (Application-Specific Integrated Circuit, ASIC), anda field programmable gate array (Field Programmable Gate Array, FPGA).In addition, the processor 10 may alternatively be a combination of aplurality of processors.

Further embodiments of the present invention are provided in thefollowing. It should be noted that the numbering used in the followingsection does not necessarily need to comply with the numbering used inthe previous sections.

1. A reference signal sending method, wherein the method comprises:

generating, by a first device, a tracking reference signal, wherein thetracking reference signal corresponds to a demodulation reference signalDMRS port that is used by the first device when the first device sendsdata to a second device, and the tracking reference signal is used totrack a phase change experienced by a tracking reference signal when thetacking reference signal is transmitted on a channel corresponding tothe DMRS port;

mapping, by the first device, the tracking reference signal to atime-frequency resource that is used by the first device when the firstdevice sends the data to the second device through the DMRS port,wherein the tracking reference signal is mapped to at least twomodulation symbols on a same frequency resource in one transmissionslot; and

sending, by the first device, the tracking reference signal mapped tothe time-frequency resource to the second device.

2. The method according to embodiment 1, wherein there are at least twotracking reference signals; and

correspondingly, at least two of the at least two tracking referencesignals are mapped to different frequency resources in thetime-frequency resource.

3. The method according to embodiment 1, wherein there are at least twotracking reference signals; and

correspondingly, at least two of the at least two tracking referencesignals are mapped to a same frequency resource in the time-frequencyresource.

4. The method according to any one of embodiments 1 to 3, wherein whenat least two DMRS ports are used by the first device when the firstdevice sends the data to the second device, each of the at least twoDMRS ports corresponds to one tracking reference signal.

5. The method according to embodiment 4, wherein at least two of the atleast two DMRS ports correspond to a same tracking reference signal.

6. The method according to embodiment 5, wherein the at least two DMRSports corresponding to the same tracking reference signal arequasi-co-located.

7. The method according to any one of embodiments 1 to 6, wherein anantenna port associated with the tracking reference signal and the DMRSport are quasi-co-located.

8. The method according to any one of embodiments 1 to 7, wherein aquantity of tracking reference signals is related to a quantity oftime-frequency resources.

9. The method according to any one of embodiments 1 to 8, wherein themethod further comprises:

receiving, by the first device, first indication information sent by thesecond device, wherein the first indication information is used toinstruct the first device to send the tracking reference signal; and

correspondingly, the generating, by a first device, a tracking referencesignal specifically comprises:

generating, by the first device, the tracking reference signal accordingto the first indication information.

10. The method according to any one of embodiments 1 to 9, wherein themethod further comprises:

before the first device generates the tracking reference signal,receiving, by the first device, second indication information sent bythe second device, wherein the second indication information is used toindicate a quantity of tracking reference signals that need to begenerated.

11. The method according to embodiment 10, wherein the second indicationinformation comprises resource scheduling information used to indicatethe time-frequency resource, and the quantity of tracking referencesignals that need to be generated by the first device is specificallydetermined based on the quantity of time-frequency resources indicatedby the resource scheduling information.

12. The method according to any one of embodiments 1 to 11, wherein themethod further comprises:

before the first device generates the tracking reference signal,receiving, by the first device, third indication information sent by thesecond device, wherein the third indication information is used toindicate a location to which the tracking reference signal is mapped inthe time-frequency resource; and

correspondingly, the mapping, by the first device, the trackingreference signal to a time-frequency resource that is used by the firstdevice when the first device sends the data to the second device throughthe DMRS port specifically comprises:

mapping, by the first device, the tracking reference signal to thelocation that is in the time-frequency resource and that is indicated bythe third indication information.

13. The method according to any one of embodiments 1 to 12, wherein themethod further comprises:

before the first device generates the tracking reference signal,receiving, by the first device, fourth indication information sent bythe second device, wherein the fourth indication information is used toindicate the tracking reference signal corresponding to the DMRS port;and

correspondingly, the generating, by a first device, a tracking referencesignal specifically comprises:

generating, by the first device, the tracking reference signal indicatedby the fourth indication information.

14. The method according to any one of embodiments 1 to 8, wherein themethod further comprises:

before the first device generates the tracking reference signal,determining, by the first device based on the quantity of time-frequencyresources, a quantity of tracking reference signals that need to begenerated; and

correspondingly, the generating, by a first device, a tracking referencesignal comprises: generating, by the first device, the determinedquantity of tracking reference signals.

15. The method according to any one of embodiments 1 to 8 or embodiment14, wherein the mapping, by the first device, the tracking referencesignal to a time-frequency resource that is used by the first devicewhen the first device sends the data to the second device through theDMRS port specifically comprises:

when at least two tracking reference signals are generated, determining,by the first device, a location to which each tracking reference signalis mapped in the time-frequency resource; and

mapping each tracking reference signal to the time-frequency resourcebased on the determined location.

16. The method according to any one of embodiments 1 to 8, embodiment14, or embodiment 15, wherein the method further comprises:

before the first device sends the tracking reference signal mapped tothe time-frequency resource to the second device, sending, by the firstdevice, fifth indication information to the second device, wherein thefifth indication information is used to indicate that the first devicesends the tracking reference signal on the time-frequency resource.

17. The method according to any one of embodiments 1 to 8 or embodiments14 to 16, wherein the method further comprises:

before the first device sends the tracking reference signal mapped tothe time-frequency resource to the second device, sending, by the firstdevice, sixth indication information to the second device, wherein thesixth indication information is used to indicate the quantity oftracking reference signals.

18. The method according to any one of embodiments 1 to 8 or embodiments14 to 17, wherein the method further comprises:

before the first device sends the tracking reference signal mapped tothe time-frequency resource to the second device, sending, by the firstdevice, a seventh indication information to the second device, whereinthe seventh indication information is used to indicate a location towhich the tracking reference signal is mapped in the time-frequencyresource.

19. The method according to any one of embodiments 1 to 8 or embodiments14 to 18, wherein the method further comprises:

before the first device sends the tracking reference signal mapped tothe time-frequency resource to the second device, sending, by the firstdevice, eighth indication information to the second device, wherein theeighth indication information is used to indicate the tracking referencesignal corresponding to the DMRS port.

20. A communications device, wherein the communications devicecomprises:

a processor, configured to generate a tracking reference signal, whereinthe tracking reference signal corresponds to a DMRS port that is used bythe communications device when the communications device sends data, andthe tracking reference signal is used to track a phase changeexperienced by a tracking reference signal when the tracking referencesignal is transmitted on a channel corresponding to the DMRS port; andfurther configured to map the tracking reference signal to atime-frequency resource that is used by the communications device whenthe communications device sends the data through the DMRS port, whereinthe tracking reference signal is mapped to at least two modulationsymbols on a same frequency resource in one transmission slot; and

a transceiver, configured to send the tracking reference signal mappedto the time-frequency resource.

21. The communications device according to embodiment 20, wherein thereare at least two tracking reference signals; and

correspondingly, at least two of the at least two tracking referencesignals are mapped to different frequency resources in thetime-frequency resource.

22. The communications device according to embodiment 20, wherein thereare at least two tracking reference signals; and

correspondingly, at least two of the at least two tracking referencesignals are mapped to a same frequency resource in the time-frequencyresource.

23. The communications device according to any one of embodiments 20 to22, wherein when at least two DMRS ports are used by the communicationsdevice when the communications device sends the data, each of the atleast two DMRS ports corresponds to one tracking reference signal.

24. The communications device according to embodiment 23, wherein atleast two of the at least two DMRS ports correspond to a same trackingreference signal.

25. The communications device according to embodiment 24, wherein the atleast two DMRS ports corresponding to the same tracking reference signalare quasi-co-located.

26. The communications device according to any one of embodiments 20 to25, wherein an antenna port associated with the tracking referencesignal and the DMRS port are quasi-co-located.

27. The communications device according to any one of embodiments 20 to26, wherein a quantity of tracking reference signals is related to aquantity of time-frequency resources.

28. The communications device according to any one of embodiments 20 to27, wherein the transceiver is further configured to receive firstindication information, wherein the first indication information is usedto instruct the communications device to send the tracking referencesignal; and

correspondingly, the processor is specifically configured to generatethe tracking reference signal according to the first indicationinformation.

29. The communications device according to any one of embodiments 20 to28, wherein the transceiver is further configured to:

receive second indication information before the processor generates thetracking reference signal, wherein the second indication information isused to indicate a quantity of tracking reference signals that need tobe generated.

30. The communications device according to embodiment 29, wherein thesecond indication information comprises resource scheduling informationused to indicate the time-frequency resource, and the quantity oftracking reference signals that need to be generated is specificallydetermined based on the quantity of time-frequency resources indicatedby the resource scheduling information.

31. The communications device according to any one of embodiments 20 to30, wherein the transceiver is further configured to:

receive third indication information before the processor generates thetracking reference signal, wherein the third indication information isused to indicate a location to which the tracking reference signal ismapped in the time-frequency resource; and

correspondingly, the processor is specifically configured to map thetracking reference signal to the location that is in the time-frequencyresource and that is indicated by the third indication information.

32. The communications device according to any one of embodiments 20 to31, wherein the transceiver is further configured to receive fourthindication information, wherein the fourth indication information isused to indicate the tracking reference signal corresponding to the DMRSport; and

correspondingly, the processor is specifically configured to generatethe tracking reference signal indicated by the fourth indicationinformation.

33. The communications device according to any one of embodiments 20 to27, wherein the processor is further configured to:

before the processor generates the tracking reference signal, determine,based on the quantity of time-frequency resources, a quantity oftracking reference signals that need to be generated; and

correspondingly, that a processor is specifically configured to generatethe determined quantity of tracking reference signals.

34. The communications device according to any one of embodiments 20 to27 or embodiment 33, wherein the processor is specifically configuredto:

when at least two tracking reference signals need to be generated,determine a location to which each tracking reference signal is mappedin the time-frequency resource; and

map each tracking reference signal to the time-frequency resource basedon the determined location.

35. The communications device according to any one of embodiments 20 to27, embodiment 33, or embodiment 34, wherein the transceiver is furtherconfigured to send fifth indication information, wherein the fifthindication information is used to indicate that the communicationsdevice sends the tracking reference signal on the time-frequencyresource.

36. The communications device according to any one of embodiments 20 to27 or embodiments 33 to 35, wherein the transceiver is furtherconfigured to:

send sixth indication information before sending the tracking referencesignal mapped to the time-frequency resource, wherein the sixthindication information is used to indicate the quantity of the trackingreference signals.

37. The communications device according to any one of embodiments 20 to27 or embodiments 33 to 36, wherein the transceiver is furtherconfigured to:

send a seventh indication information before sending the trackingreference signal mapped to the time-frequency resource, wherein theseventh indication information is used to indicate a location to whichthe tracking reference signal is mapped in the time-frequency resource.

38. The communications device according to any one of embodiments 20 to27 or embodiments 33 to 37, wherein the transceiver is furtherconfigured to:

send eighth indication information before sending the tracking referencesignal mapped to the time-frequency resource, wherein the eighthindication information is used to indicate the tracking reference signalcorresponding to the DMRS port.

A person of ordinary skill in the art may understand that all or some ofthe steps of the foregoing methods may be implemented by a programinstructing related hardware. The program may be stored in a computerreadable storage medium. The computer readable storage medium is, forexample, a ROM, a RAM, or an optical disc.

To sum up, the foregoing descriptions are merely embodiments of thepresent invention, but are not intended to limit the protection scope ofthe present invention. Any modification, equivalent replacement,improvement, or the like made without departing from the spirit andprinciple of the present invention shall fall within the protectionscope of the present invention.

1. A reference signal sending method, wherein the method comprises:mapping, by a first device, a tracking reference signal to atime-frequency resource, wherein the tracking reference signal is mappedto at least two modulation symbols on a same frequency resource in onetransmission slot, wherein the same frequency resource comprises asubcarrier, and the subcarrier is determined based on an offset valuethat is calculated based on an identifier (ID) of the first device; andsending, by the first device, the tracking reference signal mapped tothe time-frequency resource to a second device.
 2. The method accordingto claim 1, wherein the tracking reference signal corresponds to ademodulation reference signal (DMRS) port that is used by the firstdevice when the first device sends data to a second device, and thetracking reference signal is used to track a phase change experienced bya tracking reference signal when the tacking reference signal istransmitted on a channel corresponding to the DMRS port.
 3. The methodaccording to claim 2, wherein when at least two DMRS ports are used bythe first device when the first device sends the data to the seconddevice, each of the at least two DMRS ports corresponds to one trackingreference signal.
 4. The method according to claim 3, wherein at leasttwo of the at least two DMRS ports correspond to a same trackingreference signal.
 5. The method according to claim 4, wherein the atleast two DMRS ports corresponding to the same tracking reference signalare quasi-co-located.
 6. The method according to claim 2, wherein anantenna port associated with the tracking reference signal and the DMRSport are quasi-co-located.
 7. The method according to claim 2, whereinthe method further comprises: before the first device generates thetracking reference signal, receiving, by the first device, thirdindication information sent by the second device, wherein the thirdindication information is used to indicate a location to which thetracking reference signal is mapped in the time-frequency resource; andcorrespondingly, the mapping, by the first device, the trackingreference signal to a time-frequency resource that is used by the firstdevice when the first device sends the data to the second device throughthe DMRS port specifically comprises: mapping, by the first device, thetracking reference signal to the location that is in the time-frequencyresource and that is indicated by the third indication information. 8.The method according to claim 2, wherein the mapping, by the firstdevice, the tracking reference signal to a time-frequency resource thatis used by the first device when the first device sends the data to thesecond device through the DMRS port specifically comprises: when atleast two tracking reference signals are generated, determining, by thefirst device, a location to which each tracking reference signal ismapped in the time-frequency resource; and mapping each trackingreference signal to the time-frequency resource based on the determinedlocation.
 9. The method according to claim 2, wherein the method furthercomprises: before the first device sends the tracking reference signalmapped to the time-frequency resource to the second device, sending, bythe first device, a seventh indication information to the second device,wherein the seventh indication information is used to indicate alocation to which the tracking reference signal is mapped in thetime-frequency resource.
 10. The method according to claim 2, whereinthe method further comprises: before the first device sends the trackingreference signal mapped to the time-frequency resource to the seconddevice, sending, by the first device, eighth indication information tothe second device, wherein the eighth indication information is used toindicate the tracking reference signal corresponding to the DMRS port.11. A communications device, wherein the communications devicecomprises: a processor, configured to map a tracking reference signal toa time-frequency resource, wherein the tracking reference signal ismapped to at least two modulation symbols on a same frequency resourcein one transmission slot, wherein the same frequency resource comprisesa subcarrier, the subcarrier is determined based on an offset value thatis calculated based on an identifier (ID) of the first device; and atransceiver, configured to send the tracking reference signal mapped tothe time-frequency resource.
 12. The communications device according toclaim 10, wherein the tracking reference signal corresponds to a DMRSport that is used by the communications device when the communicationsdevice sends data, and the tracking reference signal is used to track aphase change experienced by a tracking reference signal when thetracking reference signal is transmitted on a channel corresponding tothe DMRS port.
 13. The communications device according to claim 12,wherein when at least two DMRS ports are used by the communicationsdevice when the communications device sends the data, each of the atleast two DMRS ports corresponds to one tracking reference signal. 14.The communications device according to claim 13, wherein at least two ofthe at least two DMRS ports correspond to a same tracking referencesignal.
 15. The communications device according to claim 14, wherein theat least two DMRS ports corresponding to the same tracking referencesignal are quasi-co-located.
 16. The communications device according toclaim 12, wherein an antenna port associated with the tracking referencesignal and the DMRS port are quasi-co-located.
 17. The communicationsdevice according to claim 12, wherein the transceiver is furtherconfigured to: receive third indication information before the processorgenerates the tracking reference signal, wherein the third indicationinformation is used to indicate a location to which the trackingreference signal is mapped in the time-frequency resource; andcorrespondingly, the processor is specifically configured to map thetracking reference signal to the location that is in the time-frequencyresource and that is indicated by the third indication information. 18.The communications device according to claim 12, wherein the transceiveris further configured to receive fourth indication information, whereinthe fourth indication information is used to indicate the trackingreference signal corresponding to the DMRS port; and correspondingly,the processor is specifically configured to generate the trackingreference signal indicated by the fourth indication information.
 19. Thecommunications device according to claim 12, wherein the transceiver isfurther configured to: send a seventh indication information beforesending the tracking reference signal mapped to the time-frequencyresource, wherein the seventh indication information is used to indicatea location to which the tracking reference signal is mapped in thetime-frequency resource.
 20. A non-transitory computer readable storagemedium, wherein the computer readable storage medium stores a computerprogram, and when the computer program is run on a computer, thecomputer performs a method for sending a reference signal, the methodcomprising: mapping a tracking reference signal to a time-frequencyresource, wherein the tracking reference signal is mapped to at leasttwo modulation symbols on a same frequency resource in one transmissionslot, wherein the same frequency resource comprises a subcarrier, andthe subcarrier is determined based on an offset value that is calculatedbased on an identifier (ID) of the first device; and Sending thetracking reference signal mapped to the time-frequency resource to asecond device.